Deposition and post-depositional processes affecting snow composition at Illimani (Bolivia), a high altitude tropical site.
Abstract
Meteorological experiments and daily surface snow sampling have been conducted in May 2001, February, May and October 2002, at Illimani (Bolivia, 16 oS, 6340m a.s.l), at the same site where two deep ice cores were extracted in 1999. The aim of the study is to better understand to what extent sublimation processes influence the chemical and isotopic composition of the deposited snow. Moreover, since May 2002, an aerosol sampling device has been installed about 40km North of Illimani at 4750m a.s.l., in order to follow the annual cycle of the total atmospheric aerosol composition (mean value over 2 days). In this region, the year may be divided into a wet season (November-April) with high precipitation and a dry season (May-October) characterised by low accumulation and strong sublimation. The measured accumulation over the period May 2001- May 2002 totals 230cm of snow (80cm w.e.) with at least 60cm (21cm w.e.) deposited during the dry period. Chemical analysis reveals a strong seasonality in snow composition, with low concentrations during the wet season and very high peaks for all chemical species during the dry season. Sublimation, actually responsible for an enrichment of all the species in the surface layer during the dry season, is not strong enough to explain these very high peaks. In addition to higher atmospheric concentrations at this time of the year, the role of dry deposition during that season could be more important. An additional interesting result is the contrast observed in the ratios of the different ions depending on the season: NH_4^+, SO_4--, Ca++, Na^+ and Cl^- are enriched during the dry season compared to the wet season, where H^+, HCOO^-, NO_3^- and NH_4^+ are the dominant species. NH_4^+ and SO_4-- were found dominant in the aerosol composition of May 2002, in agreement with the chemistry of snow observed for the dry season. Further snow and aerosol analyses are expected to provide more information on the sources of the chemical species trapped in the snow and on their deposition processes.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....2708B